OpenStack / Cloud / Virtualizaton / Linux

My 2 Rules of a Two Host ESX Cluster

Unfortunately for me I had the misfortune of learning that a two node ESX cluster is quite a fickle beast.

First off let me start by saying that this particular cluster is non-production, as my main production cluster has 8 nodes, and my secondary production cluster has 3 nodes. Less nodes often means less maintenance, which is why, I guess, that I have not run across these quirks before. So here are my new rules for a two node cluster…

Rule #1. No DRS Rules. Having a DRS rule to keep virtual machines separate is stupid if you have only two nodes in your cluster. Try putting one of the nodes in maintenance mode with this rule in place. It will not work. Plus it will not tell you why it is not working. Plus if you loose one of your ESX hosts, HA will not be able to start these two guests on the single node.

Rule #2. If you are going to put a node in maintenance mode, disable HA across your cluster first. Otherwise you are going to break HA on your other node (resulting in an HA error on your active node) and you are not going to be able to bring your node out of maintenance mode.